Transparent conductors are widely used in the flat-panel display industry to form electrodes that are used to electrically switch the light-emitting or light-transmitting properties of a display pixel, for example in liquid crystal or organic light-emitting diode displays. Transparent conductive electrodes are also used in touch-screens in conjunction with displays. In such applications, the transparency and conductivity of the transparent electrodes are important attributes. In general, it is desired that transparent conductors have a high transparency (for example, greater than 90% in the visible spectrum) and a high conductivity (for example, less than 10 ohms/square).
Typical prior-art conductive electrode materials include indium tin oxide (ITO) and very thin layers of metal, for example silver or aluminum or metal alloys including silver or aluminum. These materials are coated, for example by sputtering or vapor deposition, and patterned on display or touch-screen substrates, such as glass. However, the current-carrying capacity of such electrodes is limited, thereby limiting the amount of power that can be supplied to the pixel elements. Moreover, the substrate materials are limited by the electrode material deposition process (e.g. sputtering). Thicker layers of metal oxides or metals increase conductivity but reduce the transparency of the electrodes.
Various methods of improving the conductivity of transparent conductors are taught in the prior art. For example, issued U.S. Pat. No. 6,812,637 entitled “OLED Display with Auxiliary Electrode” by Cok, describes an auxiliary electrode to improve the conductivity of the transparent electrode and enhance the current distribution. Such auxiliary electrodes are typically provided in areas that do not block light emission, e.g., as part of a black-matrix structure.
It is also known in the prior art to form conductive traces using nano-particles comprising, for example silver. The synthesis of such metallic nano-crystals is known. For example, issued U.S. Pat. No. 6,645,444 entitled “Metal nano-crystals and synthesis thereof” describes a process for forming metal nano-crystals optionally doped or alloyed with other metals. U.S. Patent Application Publication No. 2006/0057502 entitled “Method of forming a conductive wiring pattern by laser irradiation and a conductive wiring pattern” describes fine wirings made by drying a coated metal dispersion colloid into a metal-suspension film on a substrate, pattern-wise irradiating the metal-suspension film with a laser beam to aggregate metal nano-particles into larger conductive grains, removing non-irradiated metal nano-particles, and forming metallic wiring patterns from the conductive grains. However, such wires are not transparent and thus the number and size of the wires limits the substrate transparency as the overall conductivity of the wires increases.
Touch-screens with transparent electrodes are widely used with electronic displays, especially for mobile electronic devices. Such prior-art devices typically include a touch-screen mounted over an electronic display that displays interactive information. Referring to FIG. 20, a display 310, for example prior-art liquid-crystal display 50 or organic light-emitting diode display 60 has a touch-screen 70 affixed to the surface of display 50, 60 through which light L is emitted or reflected. Numerous examples of displays with touch screens are known, for example U.S. Patent Publication No. 2011/0187677 discloses a liquid crystal display with an integrated touch-screen.
Referring to FIG. 21, a prior-art display and touch-screen system 300 using capacitive touch detection includes a display 310 with a corresponding touch screen 70 mounted with the display 310 so that information displayed on the display 310 can be viewed through the touch screen 70. Graphic elements displayed on the display 310 are selected, indicated, or manipulated by touching a corresponding location on the touch screen 70. The touch screen 70 includes a first transparent substrate 322 with first transparent electrodes 330 formed in the x-dimension on the first transparent substrate 322 and a second transparent substrate 326 with second transparent electrodes 332 formed in the y-dimension on the second transparent substrate 326 facing the x-dimension first transparent electrodes 330. A dielectric layer 324 is located between the first and second transparent substrates 322, 326 and first and second transparent electrodes 330, 332. The first and second pad areas 328, 329 are separated into different parallel planes by the dielectric layer 324. The first and second transparent electrodes 330, 332 have a variable width and extend in orthogonal directions (for example as shown in U.S. Patent Publication Nos. 2011/0289771 and 2011/0099805). When a voltage is applied across the first and second transparent electrodes 330, 332, electric fields are formed between the first pad areas 328 of the x-dimension first transparent electrodes 330 and the second pad areas 329 of the y-dimension second transparent electrodes 332.
A display controller 342 connected through electrical buss connections 336 controls the display 310 in coordination with a touch-screen controller 340. The touch-screen controller 340 is connected through electrical buss connections 336 and wires 334 and controls the touch screen 70. The touch-screen controller 340 detects touches on the touch screen 70 by sequentially electrically energizing and testing the x-dimension first and y-dimension second transparent electrodes 330, 332. Changes in capacitance between the x-dimension first and y-dimension second transparent electrodes 330, 332 can indicate a touch.
Since touch-screens 70 are largely transparent, any electrically conductive materials located in the transparent portion of the touch-screen 70 either employ transparent conductive materials (for example, transparent conductive metal oxides such as indium tin oxide) or employ conductive elements that are too small to be readily resolved by the eye of a touch-screen user. Transparent conductive metal oxides are well known in the display-and-touch-screen industry and have a number of disadvantages, including inadequate transparency and conductivity and a tendency to crack under mechanical or environmental stress. Thus, touch-screens including very fine patterns of conductive elements, such as metal wires or conductive traces are useful. For example, U.S. Patent Publication No. 2011/0007011 teaches a capacitive touch screen with a mesh electrode, as does U.S. Patent Publication No. 2010/0026664.
Referring to FIG. 22, a prior-art x- or y-dimension first or second variable-width transparent electrode 330, 332 includes a micro-pattern 356 of micro-wires 350 arranged in a rectangular grid. The micro-wires 350 are multiple very thin metal conductive traces or wires formed on the first and second transparent substrates 322, 326 to form the x- or y-dimension first or second transparent electrodes 330, 332. The micro-wires 350 are so thin that they are not readily visible to a human observer. The micro-wires 350 are typically opaque and spaced apart, so that the first or second transparent electrodes 330, 332 appear to be transparent and the micro-wires 350 are not distinguished by an observer. It is important that the micro-wires 350 are accurately located in the different layers and that the different micro-wire layers are aligned to enable efficient and consistent capacitance detection resulting from electrical field disturbances when the micro-wires 350 are energized.
Touch-screens 70 mounted over a display device 50, 60, 310, as shown in FIGS. 20, 21 are largely transparent so that a user can view displayed information through the touch-screen 70 and readily locate a point on the touch-screen 70 to touch and thereby indicate information associated with the touch. By physically touching, or nearly touching, the touch-screen 70 in a spatial touch-screen location associated with particular displayed information, a user can indicate an interest, selection, or desired manipulation of the associated particular information. The touch-screen 70 detects the touch and then electronically interacts with a computer-system processor (not shown) to indicate the touch location. The processor can then associate the touch location with displayed information to execute a programmed task associated with the information. For example, graphic elements in a computer-driven graphic user interface can be selected or manipulated with a touch-screen 70 mounted on a display 310 that displays the graphic user interface.
Touch-screens use a variety of technologies, including resistive, inductive, capacitive, acoustic, piezoelectric, and optical technologies. Such technologies and their application in combination with displays to provide interactive control of a processor and software program are well known in the art. Capacitive touch-screens are of at least two different types: self-capacitive and mutual capacitive. Self-capacitive touch-screens can employ an array of transparent electrodes, each of which in combination with a touching device (e.g. a finger or conductive stylus) forms a temporary capacitor whose capacitance can be detected. Mutual-capacitive touch-screens can employ an array of transparent electrode pairs that form capacitors whose capacitance is affected by a conductive touching device. In either case, each capacitor in the array can be tested to detect a touch and the physical location of the touch-detecting electrode in the touch-screen corresponds to the location of the touch. For example, U.S. Pat. No. 7,663,607 discloses a multipoint touch-screen having a transparent capacitive sensing medium configured to detect multiple touches or near touches that occur at the same time and at distinct locations in the plane of the touch panel and to produce distinct signals representative of the location of the touches on the plane of the touch panel for each of the multiple touches. The disclosure teaches both self- and mutual-capacitance touch-screens.
Polarizers are used in the optical sciences to control light transmission and orientation. Liquid crystal displays, for example, use polarizers to control the transmission or reflection of light in cooperation with electrically controllable liquid crystals. Organic light emitting diode (OLED) displays are known to use circular polarizers to reduce ambient reflection from the display as taught, for example, in U.S. Patent Publication No. 2008/0129189. It is important to reduce the number of layers and elements in display systems including displays, touch-screens, and light-control layers such as polarizers in order to reduce unwanted reflection, for example of ambient light. It is also important to reduce weight and thereby enhance portability and to reduce cost of such display systems.
The use of polarizing layers in conjunction with liquid crystal displays is known in the art, for example in U.S. Patent Publication No. 2011/0169767, U.S. Pat. No. 6,395,863, U.S. Pat. No. 6,707,450, and U.S. Patent Publication No. 2006/0262236. These various references describe polarizing layers either above or below a touch screen and affixed to the viewing side of a liquid crystal display to improve the contrast of the display in the presence of ambient illumination. U.S. Patent Publication No. 2010/0123672 describes a polarizer above a resistive touch screen together with an OLED display. However, such designs add additional weight, thickness, and cost to a display system.
There is a need, therefore, for an improved method and apparatus for providing touch response and light control for touch-screen display systems.